Pipelines used to transport products such as oil require periodic maintenance which involves cleaning their outer surfaces and providing them with protective coating, e.g., coating for protecting the outer surfaces of the pipes from corrosion.
Currently, each pipeline section is exposed by digging at the sides and under the pipeline, to distance the outer surfaces of the pipes from the surrounding ground sufficiently to permit to carry out on said outer surfaces the required maintenance operations. In many cases, the pipeline is laid in or crosses hard ground, such as rock formations, which is very difficult to dig out, and requires lengthy and expensive operations. It will be appreciated that while the ground may have been comminuted to some extent on the sides, when a trench was dug for the laying of the pipeline, the bottom of the trench is intact and can be formed by a hard rock mass. In addition, digging underneath the pipeline in any ground type will compromise the integrity of the trench bed and additional costs are incurred in restoring the trench bed to a state suitable for supporting the pipeline.
It will be appreciated that any damage to a pipeline, involving failure thereof and spillage of the transported liquid, would constitute, apart from the economical damages, a major economical disaster, and therefore those responsible will never carry into practice a maintenance method that involves even a very small probability of such damage and failure.
WO 01/90623 attempts to overcome the above-mentioned difficulties by disclosing an apparatus which comprises a lifting frame having four telescopic legs and a transverse top beam, telescopic lifting arms supported in the top beam, chains connected to the lifting arms for engaging the bottom of the pipeline, a first hydraulic means for telescopically extending and retracting the legs of the lifting frame and a second hydraulic means for telescopically extending and retracting the lifting arms. However, several difficulties arise when utilizing the apparatus of WO 01/90623. Firstly, the chains that pass underneath and engage the pipe consist of a multiplicity of links that are usually not evenly arranged along the extent of the chain. Thus, a non-continuous distribution of weight occurs, such that some points in the chain may be required to endure a substantially greater amount of pressure than others. Additionally, some links may be arranged such that their narrow end juts into the pipe, thereby causing a risk of external damage to the pipe, and, in some cases, even puncturing of the pipe. Furthermore, the chain disclosed in WO 01/90623 must be strong, and therefore, is very heavy. As this chain is adapted to be lifted by human effort, a heavy chain is not desirable. Finally, due to the structure of the apparatus of WO 01/90623, at least four separate acts of digging, are required in order to put the chains in place to lift one pipe section. This is excessive in view of the above-mentioned problems involved in digging at the bottom of a pipeline trench.
It is therefore an object of the present invention to provide a lifting apparatus for oil pipelines that does not suffer a risk of compromising the structural integrity of the pipeline as it is being lifted.
It is another an object of the present invention to provide a lifting apparatus that overcomes the problems associated with the prior art.
It is another an object of the present invention to provide a lifting apparatus which is positionable by human assistance without excessive difficulty.
It is another object of the present invention to provide a lifting apparatus that supports the weight of a pipe in a continuously distributed manner.
It is another object of the present invention to provide a lifting apparatus which involves considerable savings in terms of time and costs in the maintenance of pipelines with respect to a prior art apparatus.
It is another object of the present invention to provide a lifting apparatus that can be easily operated by unskilled workers.
Other purposes and advantages of the invention will appear as the description proceeds.